Exoplanet Habitability Calculator
Enter a star’s luminosity, a planet’s orbital distance, and its albedo (reflectivity) to estimate the planet’s equilibrium temperature and whether it falls in the habitable zone.
Estimating exoplanet habitability
Whether a planet could support liquid water depends heavily on its equilibrium temperature, which is set by how much starlight it receives and how much of that light it reflects back to space rather than absorbing.
The formula
Equilibrium temperature is calculated as Teq = 278.5 × (L/L☉)0.25 × (1 − A)0.25 ÷ √a, where L is the star’s luminosity relative to the Sun, A is the planet’s albedo (reflectivity, 0 to 1), and a is orbital distance in AU. For Earth’s own values (L=1, A=0.3, a=1 AU), this correctly gives about 255 K (-18°C), the airless equilibrium temperature before accounting for Earth’s greenhouse effect. The calculator also compares the orbital distance to simplified habitable zone boundaries.
Equilibrium temperature ignores atmospheric greenhouse warming, which raises a planet’s actual surface temperature considerably (Earth’s real average surface temperature is about 288 K thanks to its atmosphere). This calculator is a simplified estimate for general astronomy education, not a definitive habitability assessment.